Oops, had missed this question! Thanks Melany for offering tips on the lines.
As far as the online booking for museum tickets - the museums themselves have created a confusing system.
They DON'T sell museum tickets directly
AT ALL.
They have "chosen" b-ticket as the "official reseller" for museum tickets but at the same time also allott tickets to other vendors, which are legitimate businesses, for selling museum tickets. The total number of tickets are thus DIVIDED among all of the vendors, including b-ticket... So b-ticket themselves can run out of tickets for a certain date and time, but another vendor have their allotted tickets still available. IF you are in Florence for a day and need tickets for that day and a particular time, you can buy tickets off other sites if you don't find them available on b-ticket and be secure in knowing they are legit!
Florence-Tickets.com is one of the top vendors of Florence museum tickets and completely legitimate but, of course, the tickets end up costing a bit more because of the extra booking commissions. This system has been created by the museum organization here in Florence (the Polo Museale) that manages the state museums, including the Uffizi and Accademia.
To make things complicated, the Firenze Card, for example, is not sold by them but by the
City of Florence.... so I think there are commissions in there as well since you don't buy directly from the museums, you just don't see them.
Anyways - our website has partnered with Florence-Tickets.com to sell museum tickets in Florence and other tours in Tuscany.... so if you buy your tickets through this link:
http://www.florence-tickets.com/museum-tickets.html?site=webp
you'll be giving a small bit of support to our website and this forum!! We appreciate any support anyone offers
As far as the lines, advance tickets do make you avoid the general line into the museums - but even in these special entrances, lines form because the museum only allows entrance every 15 minutes. So you might find a line there, but rest assured you'll get in quickly with the next batch of visitors are let in.
Also long lines form principally at the Uffizi and Accademia - most of the other museums have very manageable short lines. And yes, the Firenze Card allows visitors to skip lines but at the Uffizi they still have to wait for the next batch of visitors allowed in along with the others in the "prebooked" entrance.